The current embodiments relate to the control system for an induction machine. The current embodiments relate in particular to a feedback control system for an induction machine.
An induction machine can be used alternatively as a motor or a generator. In a drive train of a motor vehicle, an induction machine can be used depending on the needs e.g. for driving or for recovery of electric energy when the motor vehicle is braking. In another embodiment, the induction machine as an integrated starter generator can be alternatively used to start a combustion engine or to transform mechanical energy from the drivetrain into electrical energy, e.g. for the electrical system of the motor vehicle. The induction machine can particularly consist of an electrically excited or permanently excited synchronous machine, a reluctance machine, an asynchronous machine or a combination of these machine types.
The induction machine consists of a number of phases P, which are usually connected in a delta or star-connection. In drive mode, predetermined voltages are produced at the connections of the induction machine, in order to influence rotation speed, rotation direction or torque of the induction machine. The phase currents that are actually flowing through the phases usually have to be measured and supplied to a control system in order to determine the voltages that have to be adjusted. A measuring of big electrical currents, such as e.g. in the above mentioned starter generator, can be time-consuming and error-prone. It is for example possible to insert a series resistor (shunt) in a supply line of one phase, at which a voltage drop can be measured that is proportional to the phase current. However, a series resistor may heat up during operation, whereby the converted electrical power quadruples in proportional to the electrical current flowing through it. The electrical power that is to be supplied to the induction machine may hereby be reduced, or problems may arise in connection with heat dissipation.